Saponifier

An alkaline chemical added to water to improve its ability to dissolve rosin flux residues.

Secondary Side

That side of the packaging and interconnecting structure furthest from layer #1 .This is commonly referred  as the “solder side” when using though-hole component mounting technology. In SMT, the secondary side may be either reflow soldered (active component) or wave soldered (passive component).

Self-alignment

Due to the surface tension of molten solder, the tendency of slightly misaligned components (during placement) to self align with respect to their land pattern during reflow soldering. This kind of correction may take care of any minor mis-alignment only.

Shadowing (Infrared Reflow)

A condition in which component bodies block radiated infrared energy from striking certain areas of the board directly. Shadowed areas receive less energy than their surroundings and may not reach desired temperatures.

Shadowing (Solder)

A condition in which solder fails to wet the surface mount device leads during the wave soldering process. Generally the trailing terminations of a component are affected, because the component body blocks the proper flow of solder. Requires proper component orientation during wave soldering to correct the problem. The body of the component may also cause “shadowing” of the terminations of another component.

Silk Screen

A screen of a closely woven solid mesh stretched over a frame and used to hold an emulsion outlining a circuit pattern. Silk screens are used in screen printing solder paste. The term is used generically to describe any screen (stainless steel or nylon) used for screen printing.

Single -Layer Board

A printed wiring board that contains metallized conductors on only one side of the board. Though-hole are unplated.

Single-Sided Assembly

A packaging and interconnecting structure with components mounted only on the primary side.

SMA, Surface Mounted Assembly

Trademark by AWI. A circuit assembly being primarily (60%) or wholly constructed using surface mount components.

SMC, Surface Mounted Components

A component designed to be mounted and soldered to lands on the surface of a packaging and interconnecting structure rather than inserted into though-holes in the structure.

SMD, Surface Mount Device

Registered trade mark of North American Philips Corporation to denote resistor, capacitor, SOIC, and SOT. The term is similar to SMC, surface mount component.

SMT, Surface Mount Technology

A method of assembling printed wiring boards or hybrid circuits, where components are mounted onto the planar surface rather than inserted into through-holes.

Snap-Off Distance

The height the stencil  or screen set above the top surface of the board (substrate) for an “off-contact” printing, which determines the amount of deflection that occurs during the snap-back action of the stencil. Snap-off distance is typically in the range of 0.003 to 0.050”. On-contact printing would have a zero snap-off distance.

SO, Small Outline

Similar to miniature dual in-line package, but with gull wing lead forms for surface mounting. Typical lead spacing:0.050”.

SOIC, Small Outline Integrated Circuit

An integrated circuit surface mount package with two parallel rows of gull wing leads, with standard spacing between leads and rows.

SOJ, Small Outline J Leaded

An integrated circuit surface mount package with two parallel rows of J-leads, with standard spacing between leads and rows. Generally used for memory devices.

Solder

A metallic alloy which has a melting temperature below 427C(800F)

Solder Balls

Small spheres of solder that remain on the board after wave or reflow soldering adhering to laminate, mask, or conductors. Solder balls are most often associated with the use of solder paste containing oxides or may be due to excessive moisture content. Baking of paste may minimize formation of solder balls, but overbaking may cause excessive balling. They are sources of electrical shorts.

Solder Bridge

An electrical short circuit between two conductors by solder that “bridges” above the dielectric.

Solder Connection

An electrical/mechanical connection which employs solder for the joining of two or more metal parts.

Solder Connection, Disturbed

Cold solder joint resulting from motion between the joined members when the solder was solidifying.

Solder Fillet

A general term used to describe the configuration of a solder joint that was formed with a component lead or termination and a PWB land pattern.

Solder Flux

A chemically active formulation capable of promoting the wetting of metals with solder.

Solder Mask

A coating applied over selected parts of a PCB that acts as a mask to prevent solder flow in the covered areas.

Solder Paste

A homogeneous combination of minute mesh size controlled solder particles (spherical or nearly spherical), flux, solvent, and a gelling or suspension agent used in surface mount reflow soldering. Solder paste can be deposited on a substrate via solder dispensing and screen or stencil printing. The constituents are added so that the viscosity, thickness, slumping, drying rate, etc. are controlled resulting in acceptable solder joint.

Solder Side

A term used in through-hole technology to indicate the soldered side of the PWB. See Primary Side and Secondary Side.

Solder Wicking

The capillary action of molten solder to a pad or component lead. In the case of leaded packages, excessive wicking can lead to an insufficient amount of solder at the lead/pad interface. It is caused by rapid heating during reflow or excessive lead coplanarity, and is more common in the vapor phase than in IR soldering.

Solderability

The ability of a metal to be wetted by molten solder.

Soldering

A process of joining metallic surfaces with solder, without the melting of the base materials.

Solvent

Any solution capable of dissolving a solute. Within the electronic industry, the term is primarily used to describe solvents with chlorofluorochlorocarbon.

SOT, Small Outline Transistor

A discrete surface mounted transistor package available in several forms. SOT-23, a three leaded device, SOT-89, s three leaded medium current device, SOT-143, a four leaded device for gated transistors and dual diodes.

Squeegee

A straight-edge rubber (or metal) blade that wipes across the stencil or screen to force the solder paste or adhesive through the stencil or screen apertures and on the PCB in the intended pattern.

Squeegee  Print Speed

The rate at which the squeegee blade moves across the stencil during the print cycle, typically in the range  between 0.4 to 6.0 in./sec

Squeegee Pressure or Down Force

The  pressure exerted on the stencil during the print cycle, typically in  the range of one to six pounds per squeegee inch.

Squeegee Stroke

The length in inches of squeegee blade travel over the stencil.

Static Electricity

An electric charge that has accumulated or built up on the surface of a material. The material may be conductive or nonconductive. In conductors the charge can pass through the material. In nonconductors the charge cannot pass and is in effect locked in place hence the term static electricity.

Static-dissipative materials

Electrostatic damage-preventing materials having surface resistivities not less than 105 but not greater than 109 ohm/cm².

Stencil

A thin sheet material (metal) with a circuit land pattern cut into the material. The most common material is stainless steel. Used for printing solder paste on a screen printer in lieu of a silk screen.

Surface Mount IC Component

Component packages having lead spacing from 0.8mm (0.03”) to 1.3mm (0.05”) center to center.

Surface Mounting

The  electrical connection of components to the surface of a conductive pattern that does not utilize component lead holes.

Surfactant

Contraction of “surface active agent” . a chemical added to water in order to lower surface tension and allow penetration of water under tighter spaces.